With recent extended application fields of semiconductor devices, a surface mount scheme has been widely used for mounting semiconductor devices on a printed circuit board. A lead frame is mainly used for assembling a semiconductor device. A chip is mounted on the bed of a lead frame, with the chip being electrically connected to the lead frame by means of wire bonding.
There are known lead frames capable of mounting a plurality of semiconductor chips. The structure of such lead frames is shown in FIGS. 1A, 1B, 2A, and 2B by way of example. FIGS. 1B and 2B are top views showing such lead frames LF mounting a semiconductor chip, and FIGS. 1A and 2A are perspective views showing the semiconductor chips after resin molding.
Although the details of the structure of lead frames LF differs depending upon their types, all lead frames have a number of leads extending from the periphery of a lead frame toward the center thereof. A lead frame of a dual-in-line package DIP type has leads 1, 1, . . . extending from a frame portion 2. Each unit lead frame LF is partitioned by slits 3. An island (bed portion) 5 is supported near at the tip portion of leads 1 by support members (metal connectors) 6, 6 extending opposite to the island. A semiconductor pellet 4 is mounted on the bed portion 5. The bed portion 5 is integrally formed with the frame portion 2 via the support members 6, 6. The bed portion is formed wider than the lead 1. The semiconductor pellet 4 mounted on the lead frame LF is sealed with a package (enclosure) 7 made of resin by a predetermined process. The perspective views of FIGS. 1A and 2A show the final shape of the finished semiconductor devices. The portion of a lead 1 projecting out of the package 7 is bent by a predetermined angle. The bent portion may take a shape different from those shown in FIGS. 1A and 2A depending upon the type of each surface mount device. A semicircular notch 8a shown in FIG. 1A and a circular recess 8b in the package 7 shown in FIG. 2A are used for indicating the direction of a package and the numbers of lead pins.
It is also known that a plurality of semiconductor chips are mounted on islands of a lead frame of a resin sealed semiconductor package. The size of a chip is generally wider than the width of a lead. It is therefore necessary to make the island formed on a lead wider than the width of a lead. In this case, the ratio of the lead frame metal area to the whole area of a resin sealed package becomes considerably large, lowering the packaging density.
The wiring pattern of leads within the package has less space at the inner end portions of leads near the chip. Therefore, in many cases it is impossible to form another island near the inner end portion of a lead. However, there is often a space for forming an island at the intermediate portion between the inner end portion and the outer end portion. It is also known that an island is formed at such an intermediate portion in order to mount a plurality of chips.
Conventionally, it has been necessary in general to prepare commonly-called suspension pins which prevent a semiconductor device from being dismounted from the lead frame while performing lead forming after resin molding and electrode lead cutting. Therefore, in many cases there is no space for forming suspension pins if a plurality of chips are to be mounted, so that it is impossible to manufacture a resin sealed semiconductor device having a plurality of chips mounted thereon, i.e., to manufacture a highly value-added semiconductor device.